In a conventional ink jet head, an external extension electrode extends from an ink chamber electrode, which is provided within an ink chamber, to the outside of the ink chamber. The external extension electrode is connected to an external circuit. The ink chamber electrode is thus electrically connected with the external circuit.
A method of providing an ink chamber electrode of a conventional ink jet head extending to the outside of the ink chamber is described below with reference to FIG. 14.
First, one of the main surfaces of a piezoelectric element that has been polarized in the direction of its depth is laminated with a dry film resist. The piezoelectric element is then halfway-diced using the dicing blade of a dicer. This forms an ink chamber 250 in the halfway-diced portion. Moreover, removal of the dicing blade from the halfway-diced piezoelectric element leaves an arc portion 251 at the rear end of the ink chamber. Halfway-dicing is further repeated for a plurality of times, producing a plurality of ink chambers 250 extending parallel to each other.
This provides an ink chamber array 400 having a plurality of ink chambers 250. Subsequently, a metal that is to be an electrode material, such as Al or Cu, is deposited in an oblique manner in a direction that is perpendicular to the direction in which the plurality of ink chambers 250 extend and that is oblique with respect to a main surface of ink chamber array 400. This operation is made in two oblique directions with respect to the direction of ink chambers 250. In this way, ink chamber electrodes, each formed of a metal film 350, are formed on a surface of ink chamber partition 300. At this stage, the dry film resist and ink chamber partitions 300 between ink chambers 250 exhibit a “masking effect”. This provides a metal film 350 on an inner side of ink chamber 250 with a height of less than about half that of the inner side of ink chamber 250.
Metal film 350 is also formed in the portion of the rear end of ink chamber 250 with a curved surface (arc portion) 251 and in the portion of opening of the dry film resist in a flat portion 260. Subsequently, only the dry film resist on flat portion 310 atop each ink chamber partition 300 separating ink chambers 250 is removed, thereby establishing, in arc portion 251, an electrical connection between those metal films 350 that are opposed to each other within ink chamber 250.
Subsequently, as shown in FIG. 15, a cover 210 with an ink supply through hole 209 is bonded to ink chamber array 400. In addition, a nozzle plate 211 with nozzles 212 is bonded to ink chamber array 400. Thus, actuator 200 is obtained.
Actuator 200 provides for the Shear mode drive, where voltages in opposite phase are applied to the two respective ink chamber electrodes, each formed of one of opposing metal films 350 which is provided on the respective one of both inner sides of ink chamber partition 300 separating ink chambers 250. This causes ink chamber partition 300 to be bent angularly on the border between the region having the ink chamber electrode and the region without it, causing a change in the volume of ink chamber 250. This in turn causes a change in the pressure of ink within ink chamber 250. As a result, ink drops are ejected from very small nozzle 212 disposed at the tip end of ink chamber 250.
In the conventional structure of an ink jet head described above, active area 252 that contributes to the ejection of ink is only located between ink supply through hole 209 and the tip end. In other words, the region between ink supply through hole 209 and the rear end does not contribute to ink ejection. Further, metal film 350 in arc portion 251 and flat portion 260 electrically connects those two ink chamber electrodes that oppose each other in ink chamber 250. This provides an electrical connection between an electrode that is conductive with a driving IC 115 and metal film 350.
The above arrangement for ink jet heads suffers from the high material cost due to an excessively large portion that is not included in active area 252 which contributes to ink injection.
Moreover, the above ink jet head requires metal film 350 to extend from within ink chamber 250 to flat portion 260 on the piezoelectric substrate of lead zirconate titanate (PZT) having a high dielectric constant. This causes a large capacitance due to the piezoelectric substrate. This in turn disturbs the driving voltages applied to the actuator for driving it. Consequently, the frequency of the driving voltages must be reduced in the conventional ink jet head, which causes difficulty in driving and printing at a high speed.
Disturbance in the waveform of the applied driving voltages may be overcome by increasing the voltages applied to the actuator. Increasing the applied voltages, however, causes increase in the heat generated in driving the actuator to raise the temperature of the actuator itself. Thus, the conventional ink jet head suffers from a changing ink viscosity which makes a stable, precise printing impossible, an increased cost of the driving IC with high applied voltages, and the difficulty of reducing power consumption.
Accordingly, a conventional method of manufacturing ink jet heads preforms an Si—N film with a low dielectric constant between the piezoelectric substrate and the ink chamber electrode in the portion that is other than active area 252 of the ink chamber electrode within ink chamber 250 of the actuator. This achieves a negligible level of capacitance in the portion other than active area 250 using the conventional method. However, PZT has a low Curie point of about 200° C., requiring an electronic cyclotron resonance-chemical vapor deposition (ECR-CVD) device, which is very expensive, in order to form an Si—N film with a low dielectric constant on PZT using a process with a low temperature. As a result, the manufacturing cost is increased in the conventional method such that inexpensive ink jet heads cannot be produced.
A technique for coping with the above problems is disclosed in Japanese Patent Laying-Open No. 9-94954, which provides an ink jet head where, as shown in FIG. 16, the portion other than active area 252 is not located on an extension line of the ink chamber in the piezoelectric substrate.
In the described technique, an ink supply through hole 110 is provided at the rear end of the active area of the piezoelectric substrate to supply ink. Each electrode 111 in the ink chamber extends externally on the ink supply side of the substrate or extends to the area of the ink ejection side of the substrate on its inner surface. This provides an electrical connection of electrode 111 in the ink chamber with electrode 112 which is conductive with a driving IC 115. In this case, no portion other than the active area for the actuator is provided on the piezoelectric substrate, decreasing the material cost for the piezoelectric substrate. However, an electrode 111 in the ink chamber extending externally on the ink supply side of the substrate or extending to the area of the ink ejection side of the substrate on its inner surface still suffers from the problem that the capacitance due to the piezoelectric substrate in the extending portion of ink chamber electrode 111 cannot be reduced.
Moreover, in the above method, electrode 111 in the ink chamber extends to be bent at 90° at a corner of the piezoelectric substrate forming the actuator.
The extension of an electrode to a side of an actuator requires a metal film to be provided on the side of the actuator such that the piezoelectric substrate is divided into small individual actuators and an extension electrode is then put into continuity with the respective pair of ink chamber electrodes. Further, a separation of the extending electrodes requires the steps of forming a uniform layer of conductor with a resist pre-patterning and then separating it into electrodes by dicing or using yttrium aluminum garnet (YAG) laser. Consequently, the process is extremely complicated and thus productivity is low, reducing the yield and increasing the production cost. Moreover, it is highly possible that an extending electrode is broken up at a bended portion of the electrode which extends from within the ink chamber to a side of the actuator, during subsequent steps or transportation of the actuator, thereby decreasing the yield and the reliability in terms of the environment.
The extension electrodes may also be formed using plating. However, the plating technique requires, similar to deposition techniques, the steps of patterning or dividing a material into electrodes. This may complicate the process.
Also, the above extension electrode as in FIG. 16 can be broken up at a bended portion of the electrode extending from within the ink chamber to a surface of the actuator because of a botched handling during subsequent steps. Consequently, the conventional ink jet head has the problems of decreased yield and less reliability in terms of the environment.